14-3-3θ Facilitates plasma membrane delivery and function of mechanosensitive connexin 43 hemichannels

Abstract

Intracellular signaling in osteocytes activated by mechanical loading is important for bone formation and remodeling. These signaling events are mediated by small modulators released from Cx43 hemichannels (HC). We have recently shown that integrin α5 senses the mechanical stimulation and induces the opening of Cx43 HC; however, the underlying mechanism is unknown. Here, we show that both Cx43 and integrin α5 interact with 14-3-3θ, and this interaction is required for the opening of Cx43 HC upon mechanical stress. Ablation of 14-3-3θ prevented the interaction between Cx43 and integrin α5, and blocked HC opening. It further decreased the transport of Cx43 and integrin α5 from the Golgi to the plasma membrane. Moreover, mechanical loading promoted the movement of Cx43 to the surface which was associated not only with an increase in 14-3-3θ levels but also its interaction with Cx43 and integrin α5. This stimulatory effect on forward transport by mechanical loading was attenuated in the absence of 14-3-3θ and majority of the Cx43 was accumulated in the Golgi. Disruption of Golgi apparatus by brefeldin A reduced the association of Cx43 and integrin α5 with 14-3-3θ, further suggesting that the interaction is likely to occur in the Golgi. Together, these results define a novel, scaffolding role of 14-3-3θ in assisting the delivery of Cx43 and integrin α5 to the plasma membrane for the formation of mechanosensitive HC in osteocytes.